This invention relates to filter cartridges and a method for their production.
Such filter cartridges are employed to filter various media. The filter cartridge comprises a permeable material, in particular a micro-filter matting which is folded in a zig-zag fashion and has a block-like form. During the filtration process the medium to be filtered passes through the filter cartridge from one edge area of the zig-zag folding in the direction of the edge area of the folding on the opposite side. The fold walls which are created by the folding of the filter material are provided with offsets which extend out on both sides of the plane of the fold walls. The offsets in the fold walls are arranged in such a way that an offset in the form of a raised portion on one fold wall is in contact with an offset in the form of a raised portion on the adjacent fold wall. Due to the folding in a zig zag fashion the offsets of the fold walls are in contact with each other and are supported in the region of the contact area.
In this way the adjacent fold walls are held apart at a set distance and a uniform flow of the medium through the filter walls is guaranteed.
A drawback of this arrangement is that pressure variations occur when the medium to be filtered passes through the filter material as the spacing between the filter walls cannot be exactly defined geometrically. This is due the forces resulting from the resistance to flow which deform the not sufficiently stable filter cartridge. In order to compensate for the greater resistance to flow the throughput of the medium to be filtered has to be made greater. In this way the operational life-span of the filter cartridge is lowered. In addition, the motor means required to throughput the medium to be filtered become increasingly noisier with increasing throughput.
The offsets in a fold wall can also only be of a limited height as the roll forming of the offsets in the filter material causes the wall thickness of the offsets to decrease. A large number of offsets also have to be positioned due to their low stability which in turn reduces the filter surface area available for the medium to be filtered to pass through. The resistance to flow thereby increases. This leads to a greater noise level in the filter plant and a shorter operational life-span thereof.